1. Field of the Invention
The present invention relates to a vane pump and an evaporative leak check system having the same.
2. Description of Related Art
In a known vane pump, a rotor having a plurality of vanes is rotated to pressurize and discharge fluid upon pressurization thereof. For example, Japanese Unexamined Patent Publication. No. 2009-138602A (corresponding to US 2009/0148329A1) teaches such a vane pump that is used to depressurize or pressurize an interior of a fuel tank in an evaporative leak check system that is used to check leakage of fuel vapor from the fuel tank. The performance of the evaporative leak check system is often influenced by a pump performance of the vane pump.
In this vane pump, a pump chamber is formed between the upper casing and the lower casing, and a rotor having vanes is rotatably received in the pump chamber. The upper casing and the lower casing are secured to a mount portion of the motor with screw members. A resilient sheet is placed between the lower casing and the mount portion of the motor. A reaction force is generated in the resilient sheet in response to a tightening force of the screws. When this reaction force is applied, the lower casing is urged against the upper casing to tightly contact against the upper casing. In this way, a fluid tightness (gas tightness or liquid tightness) of the pump chamber is improved.
The resilient sheet of the vane pump, which is disclosed in Japanese Unexamined Patent Publication No. 2009-138602A (corresponding to US 2009/0148329A1), is made of a planar resilient member having two opposed smooth planar surfaces, which are opposed to each other in a direction perpendicular to the plane of the sheet. Therefore, the reaction force, which is generated in the resilient sheet, may vary from product to product in a span of control of the tightening force generated by the screws at the time of manufacturing. When the reaction force of the resilient force substantially varies from the product to product, the fluid tightness (gas tightness or liquid tightness) of the pump chamber may possibly be excessively reduced or excessively increased. In such a case, it is difficult to place a suction pressure or discharge pressure of the vane pump immediately after the manufacturing thereof in a predetermined factory standard range thereof.
Furthermore, when a thickness of the resilient sheet is increased to reduce the amount of change (variation) in the reaction force, the size and costs of the resilient sheet may possibly be disadvantageously increased.